Integrated circuits have evolved into complex devices that include multiple levels of metal layers to electrically interconnect discrete layers of semiconductor devices on a single semiconductor chip. Recently, with the evolution of higher integration and higher density of integrated circuit components, the demand for greater speed of the data transfer rate is required. For this reason, an insulating film having low leakage current, low dielectric constant with high elastic modulus and hardness, to give the small RC delay is employed.
As the device dimensions continuously shrink, the RC time delay of the interconnect system becomes one of the most important limitation factors to the integrated circuits performance. The RC delay is directly proportional to the resistivity of the metal and the dielectric constant of the dielectric. In order to minimize the signal propagation delay, it is inevitable to use low dielectric constant materials as the inter-layer and intra-layer dielectrics (ILD).
The initial approach for providing low-dielectric films was the doping of the silicon oxide material with the other components such as fluorine that reduces the dielectric constant but only to that of about 3.5 to 3.9. Since the fluorine doped silicon oxide films offer only a small decrease in the dielectric constant, other solutions having lower dielectric constant are required. Furthermore, the stability of the fluorine doped silicon oxygen films with regard to moisture is problematic.
In an approach for providing a silicon oxide layer having a planar surface, spin-on-glass composition have been prepared utilizing polyorganosilsesquioxanes as presented in U.S. Pat. No. 4,670,299. The advantages of this film is that it has low dielectric constant such as that of 2.6 to 3.0, and also maintain the higher mechanical strengths of silicon oxide type films.
However, it would be advantageous to have a final dielectric film that combines the advantage of a film formed from organic polysilicas such as polyorgansilsesquioxanes referred to herein as POQS with an even lower dielectric constant (k<2.5). The most likely method for achieving this result is to blend the POSQ with another substance with lower dielectric constant. A substance with lower dielectric constant is air (k=1). So, in order to achieve lower dielectric constants, porosity needs to be introduced into the POSQ material. However, the process of introducing porosity is complex and is slow.
Furthermore, to reduce the size of interconnection lines and vias is to change the wiring materials from the conventional aluminum (Al) to copper (Cu) wiring having low electric resistance. However, to produce a semiconductor device having multi-layered copper wiring, a low dielectric constant insulating layer is formed as the interlayer insulating film on the copper wiring.
The use of copper as the interconnect material has various problems. For example, copper is easily diffused into the low dielectric constant insulating film from the copper wiring, thus increasing the leakage current between the upper and lower wiring.
The use of silicon carbide films as copper diffusion barrier layers has been published in U.S. Pat. No. 5,800,878. The dielectric constant of this film is about 5, and in addition it is used as copper diffusion barrier layers for 130 nm-nodes Large Scale Integration (LSI) technologies where the dielectric constant of the interlayer dielectric film is 3.
For next generation, 100 nm/65 nm-nodes Ultra Large Scale Integration (ULSI) technologies, the reduction of interconnect capacitance is important for suppressing the signal delay as well as the power consumption. Interlayer dielectric films with dielectric constant less than 2.5 are used with copper damascene structures. To decrease the effective dielectric of fine pitched lines, further reduction in the dielectric constant is necessary not only for the inter layer dielectric film itself but also the supporting dielectric films such as hard mask, etch stop layers and copper diffusion barrier layers. However, the process is difficult.
The interface between copper and copper diffusion barrier layer is known to be the key point for the electro-migration reliability of copper interconnects. The interface between copper and the copper diffusion barrier layer is the dominant diffusion path. However, there is no report on the identification of the dominant path for copper interconnects. On the other hand, the interface can be not only the dominant path but also the electro-migration induced void nucleation site.
The strength of adhesion between copper and diffusion layer would affect the electro-migration induced void nucleation because electro-migration induced void nucleates when copper atom at the interface is stripped away from the diffusion layer. It is also suggested that in order to prevent the migration of metal atoms, the film has to have a stable film stress even after being directly exposed to air at room temperature of about 20 to 30° C. Furthermore, the leakage current and dielectric constant of such film at 1 MV/cm has to be less-than that of 1×10−9 A/cm2 and less than 3.5 respectively. SiCO films with dielectric constant less than 3.5 such that the leakage current at 1 MV/cm is less than 1×10−9 A/cm2 are suggested to be suitable to substitute for such films.
Using the silicon carbide film as an etch stop film was developed and presented in U.S. Pat No. 5,800,878. A dielectric constant of the silicon carbide film is approximately 5. Silicon carbide films are applied to LSI devices using copper wiring in combination with carbon-containing silicon oxide films, whose dielectric constant is approximately 3. There are several different types of compositions for what is generally called silicon carbide films. One type is a silicon carbide film comprising Si, C and H. This film's stress and dielectric constant changes if left in the atmosphere. This is due to the oxidation of the top surface of the silicon carbide film. The method to minimize the oxidation of carbon containing materials, such as silicon carbide, with an inert gas plasma such as helium (He), Argon (Ar) is published in JP laid-open patent 2001/0060584. This inert gas plasma treatment only minimizes the top surface of the silicon carbide film from getting oxidized, however, no changes/improvements to the film properties are observed.
The method of forming nitrogen doped silicon carbide (SiCN), oxygen doped silicon carbides (SiCO) has been published in United States Patent Application Publication 2001/0030369, United States Patent Application Publication 2002/0027286, United States Patent Application Publication 2001/0051445, and United States Patent Application Publication 2001/0031563. Furthermore, these films have been proposed as copper diffusion barrier layers. Though a nitrogen doped silicon carbide layer has been proposed as a copper diffusion barrier layer with low leakage current, its dielectric constant is high such as 5.
Therefore, there is a need for a low dielectric constant film which also supports the copper diffusion barrier layers properties and is useful for the fabrication of IC devices, where the film is mechanically strong, useful at high temperatures, and is easily and quickly fabricated.